Railway traffic controlling apparatus



Oct M), 1944. G. w. BAUGHMAN 2,360,034

RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Jan. 3, 1942 X Suppl/y Bu TH CW I 2H INVENTOH Georg; ZZ/flauglzmmz H1514 TTORZVEY.

Patented Oct. 10, 1944 RAILWAY TRAFFIC CONTROLLING APPARATUS George W. Baughman, Swissvale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application January 3, 1942, Serial No. 425,550

4 Claims.

My invention relates to railway trafiic controlling apparatus and more particularly to apparatus for preventing false energization of track relays due to foreign current which may be induced in the rails of the track by propulsion conductors or other high power transmission lines which parallel the trackway.

One of the advantages possessed by alternating current track circuits employing two-element track relays is that these inherently provide foreign current protection of a high order because foreign current must be present not only in the track winding but also in the local winding and the phase relations must be correct, before any false operation is possible. The alternating current frequency employed for operating these track circuits is in all cases selected so as to differ by a substantial amount from the frequency of any adjacent transmission line likely to cause interference. In the case of alternating current propulsion, the track winding of the track relay may under certain conditions carry a considerable amount of propulsion current so that the frequency separation between the propulsion current and the track circuit signaling current must be sufficient to insure that the track circuit apparatus will not operate falsely at the maximum value of propulsion current to which the apparatus may be subjected in service. Ordinarily, the presence of propulsion current in the track winding of the track relay cannot cause false operation because these relays require simultaneous energization of both the track winding and the local or line winding from the same alternating current source. However, under certain conditions involving a broken rail, for example, the control element of a track relay may acquire a substantial propulsion potential at the same time that the local element also receives a propulsion potential from the signal transmission line upon which the track propulsion voltage has been impressed in the step-up direction through the track transformer. In the United States Patent No. 2,216,614 granted to Robert M. Gilson and George W. Baughman on October 1, 1940, are shown certain means for preventing such false operation. In that patent, however, the apparatus as shown requires a protective relay for each track circuit. My present invention is an improvement on the apparatus of the foregoing patent which makes it possible to protect all the track circuits of a group by means of a single protective relay.

Accordingly, an important object of my invention is to provide protection for several track circuitsby means of one protective relay, thus rendering the apparatus more economical and more broadly useful. A further object is to provide this protection by deenergizing the track circuit rather than the local element of the track relay. In this manner, the protection is extended more fully and the necessity for an extra line wire is removed. Other objects, purposes and features of my invention will be apparent from the description which follows.

I accomplish these objects by employin a twoelement protective relay so arranged that it controls the track circuit energy supplied to a group of track circuits at that location, all of this track circuit energy being caused to flow through the control winding of the protective relay. When the track circuit energy flows through this con-- trol winding in the direction from the signal transmission line to the track, the protective relay remains energized and so maintains the track circuits in their energized condition. Should, however, foreign current be induced in the track and the apparatus at that location be disconnected from its normal source of supply at the time (so that the foreign current potential could be stepped up through the track transformers and applied to the apparatus at that location) the direction of current flow through the control winding will be reversed so that the protective relay will release and will thus provide the necessary protection.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

The accompanying drawin is a diagrammatic view showing one form of apparatus embodying my invention as applied to the track circuits of a two-track propulsion railroad.

Referring to the drawing, the track sections IT, 2T, 3'1 and 4T represent stretches of an alternating current propulsion railway and are interconnected by means of the usual impedance bonds 113 which provide a low impedance path for the flow of propulsion current but which offer a relatively high impedance to the flow of inter-rail current so that the necessary track circuit potential can be maintained between the rails. These sections are separated from one another by the usual insulated rail joints to form track circuits which, as here shown, have a track transformer T1 supplying current at one end of the track circuit and a two-element track relay TR receiving current at the other end of the track circuit. Only two track circuits 2T and 3T are shown complete because in the illustrative embodiment of the invention shown herein, only these track circuits are protected by the protective relay PR. Track circuit IT would be protected by the protective relay at the next relay location to the left, and track circuit 4T would be similarly protected at the next relay location to the right, as viewed in the drawing. Although I have shown only a two-track road in order to simplify the disclosure, it will be apparent that use of the protective relay PR is not limited to the protection of two track circuits, this relay being capable of protecting all of the track circuits which are supplied with power from a given location. In the case of a fourtrack road, for example, four track circuits would ordinarily be protected by this relay.

The signal power is supplied in any suitable manner to the two wires of the 110 volt alternating current local bus across which are connected the local windings LW of the various track relays TR. A separate track transformer supply bus is provided at each location to be protected and the primary windings of the track transformers TT are connected across this track bus. In series with the secondary winding of each transformer is included the usual current limiting reactor X.

The protective relay PR may be a two-element alternating current relay of any suitable type although preferably it should be a frequency selective relay such as a centrifugal frequency relay which cannot be operated by currents other than those of the signaling frequency or those which closely approximate this frequency. The local element LE of this relay is energized from across the alternating current bus, and the control element CE is connected in series with the supply to the primary windings of the track transformers TTT which are energized from this particular location. The energy for these transformers is conducted over the normally closed front contacts 5 and 6 of relay PR so that it is essential for relay PR to be energized before any track circuit current can be supplied to the track circuits 2T and 3T which are protected by this relay. Resistor R is the pick-up resistor for relay PR and is connected in series with the control winding CE across the line in order that the protective relay may be picked up following a release operation. That is to say, after a release operation which causes decnergization of winding CE takes place, restoration of power to the alternating current bus causes sufiicient current to flow through the resistor R and winding CE to pick up the relay. Once contacts 5 and 6 close, the current in wind ing CE increases due to the track circuit power and the relay is held firmly energized thereafter.

The operation of the apparatus is as follows. Normally, when the alternating current bus is intact and is energized, the protective relay PR will be picked up, energizing the track transformer supply bus and the track circuits 2T and 3T so that the associated track relays will also be energized. Under this condition, even if substantial amounts of foreign current are induced or are otherwise present in the track rails, the track relays will not be falsely picked up by this current because the foreign current, though present in the track relay control windings, will not be present to any substantial degree in the local windings. I have found by calculation and by actual test in service that whenever the line bus is intact and energized, the effective impedance of the generating apparatus and other apparatus normally connected across this bus (as compared with the impedance of the apparatus connected across the line at the location to be protected) is so low as to shunt out very effectively the foreign current potential which might be stepped up through the track transformers and tend to be impressed across the line bus and thus tend to energize the local windings of the track relays. Accordingly, since the foreign current, if any, is present only in the track windings, the track relays will not be falsely operated because of their inherent design which precludes operation except when both elements are simultaneously energized by currents of identical frequency, that is, supplied from the same source. It is clear from the foregoing that false operation could result only at a time when th line bus is disconnected from its generating equipment at which time the normally present low impedance shunt path for suppressing any induced foreign current would be lacking so that the line windings LW could then become falsely energized. I

It is under conditions such as outlined above that the apparatus embodying my invention comes into play to provide protection against false operation. It will be observed that under normal conditions when the line bus is energized from its generating equipment, the relative direction of current flow through the control element CE of relay PR at a given predetermined instant may be considered as being from left to right, that is, the left-hand terminal of winding CE may be considered positive at that instant. If, however, the energy which the line bus receives comes not from the generating equipment but from foreign current in the track, then the relative direction of current flow (for the same instantaneous polarity of energization of winding LE) is reversed in the control winding CE so that under the assumed condition, the righthand terminal of winding CE may be considered positive. This reversal of the current direction in one element of the protective relay will obviously reverse the relay torque so that relay PR. will release whenever a condition exists such as would permit a foreign current potential to be impressed across the line bus.

From the foregoing, it will be apparent that I have provided protective apparatus which effectively prevents false track relay operation due to the presence of foreign alternating current in the rails and which requires only a single protective relay for safely guarding a plurality of track circuits at a given location.

Although I have herein shown and described only one form of railway traffic controlling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination with a section of railway track, a two-element alternating current track relay having one element connected so as to receive energy from the rails of said section, a normally energized alternating current transmission line, a circuit for supplying energy from said transmission line to said one element of the track relay over the rails of said section, means for supplying energy from said transmission line to the other element of said track relay to cause operation thereof, a normally picked up two-element protective relay havingone element energized from said transmission line and having the other element included in said circuit so that the track circuit energy for said track relay flows through said other element of the protective relay, and means including a contact of said protective relay for preventing the supply of energy over said circuit upon the flow of foreign current from the rails of said section into said transmission line over said circuit when said transmission line is deenergized, said foreign current causing a release of said protective relay, said first-named means excluding said contact of the protective relay.

2. In combination with a section of railway track, a two-element track relay having one element receiving energy from the rails of said section and its other element receiving energy directly from a normally energized alternating current transmission line, an energy supply circuit for supplying track circuit current from said transmission line to energize said one track relay element over the rails of said section, a normally picked up two-element protective relay having one element energized from said transmission line and having the other element included in said energy supply circuit, means controlled by said protective relay for interrupting said energy supply circuit upon the fiow of foreign current from the rails of said section into said transmission line over said energy supply circuit when said transmission line is deenergized, said foreign current causing a release of said protective relay, and an impedance connected in series with said other element of the protective relay across said transmission line to pick up the protective relay and restore said energy supply circuit upon reenergization of the transmission line.

3. In combination with a section of railway track, a normally energized alternating current transmission line, an energy supply circuit for supplying track circuit current from said transmission line to the rails of said section, a twoelement protective relay having one element energized from said transmission line and having the other element connected into said energy supply circuit in such direction that the track circuit energy passing therethrough maintains said protective relay energized, whereby in the event foreign current flows from the rails of said section over said supply circuit into said transmission line when said transmission line is deenergized the relative polarity of said two elements will be reversed so that said protecive relay will release, a front contact of said protective relay included in said energy supply circuit for interrupting said energy supply circuit due to such foreign current, means including an impedance device connected in series with said other element across said transmission line for picking up said protective relay upon reenergization of said transmission line, and a two-element track relay having one element connected to the rails of said section and its other element connected directly to said transmission line to effectively energize the track relay only when said protective relay is energized.

4. In a multiple track railroad, in combination, a plurality of track sections one for each track, a normally energized alternating current transmission line, a two-element track relay for each of said sections, each such track relay having one element connected to the rails of the respective section and its other element connected directly to said transmission line, energy supply circuit means connected to the transmission line and to the rails of said sections to normally energize each of said track relays, a twoelement protective relay having one element connected to said transmission line and its other element interposed in said energy supply circuit means, said protective relay having its elements connected to retain the relay picked up when the transmission line supplies current to the track sections and to release the relay if foreign current flows from the rails of any one of said sections to the transmission line through the energy supply circuit means when the normal energizing of the transmission line fails, a front contact of said protective relay included in said energy supply circuit means to retain the supply circuit means interrupted once the protective relay is released due to foreign current to avoid effective energization of any track relay by foreign current from any track section, and means including an impedance to connect said other element of the protective relay across the transmission line to reenergize that relay when the normal energization of the transmission line is restored.

GEORGE W. BAUGHMAN. 

